The present invention relates to a novel steam turbine blade and, more particularly to a low pressure steam turbine having rotor blades in the final stage of the low pressure steam turbine made of a 12% Cr group steel and a steam turbine power plant using the low pressure steam turbine.
At the present time, 12Crxe2x80x94Moxe2x80x94Nixe2x80x94Vxe2x80x94N steel is used for steam turbine rotor blades. In recent years, it is required from the viewpoint of energy conservation to improve the thermal efficiency of a stream turbine, and it is required from the viewpoint of space conservation to make the components compact.
Employing long-length steam turbine blades is an effective means for improving the thermal efficiency of a steam turbine and for making the components compact. Therefore, the length of low pressure steam turbine blades in the final stage is being lengthened year by year. This trend makes the use condition of the steam turbine blades severer, and accordingly a higher strength material is required because the strength of the 12Crxe2x80x94Moxe2x80x94Nixe2x80x94Vxe2x80x94N steel is insufficient. As the strength of a material for the long blade, a high tensile strength of basic mechanical property is required.
Further, the material is required to be high in strength and high in toughness from the viewpoint of securing safety against rupture.
As structural materials having a tensile strength higher than that of the conventional 12Crxe2x80x94Moxe2x80x94Nixe2x80x94Vxe2x80x94N steel (a martensite group steel), Ni based alloys and Co base alloys are generally known. However, they are not suitable for the blade material because they are worse in hot workability, in cutting workability and in vibration damping characteristic.
WO97/30272 discloses a rotor blade in the final stage of a low pressure steam turbine made of a 12% Cr group martensite steel, and a low pressure steam turbine using the turbine blades and a steam turbine power plant using the low pressure steam turbine. Further, a low pressure turbine blade having a 48-inch blade length made of 17-4PH steel for a 3000 rpm turbine is described in Technical Report of Mitsubishi Heavy Industry, Vol. 35, No. 1 (January, 1998).
Rotor blades in the final stage of the low pressure steam turbine having a blade length of 43 inches for a 3000 rpm turbine and a blade length of 35.8 inches for a 3600 rpm turbine are described in WO97/30272. However, there is no description on a length of the blade longer than the above, and there is no description on shape of the blade nor size of the low pressure steam turbine either.
Further, the above-mentioned technical report does not describe on any remedy for a longer blade nor on strength and toughness of the 17-4PH steel.
An object of the present invention is to provide a steam turbine blade made of a martensite steel having high strength and high toughness which is capable of attaining a blade length above 48 inches for a 3000 rpm turbine and above 40 inches for a 3600 rpm turbine, and a low pressure steam turbine and a steam turbine power generating plant using the steam turbine blades.
The present invention is characterized by a steam turbine blade having a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, which is made of a martensite steel having a 20xc2x0 C. V-notch impact value larger than 6 kgxc2x7m/cm2 and a 20xc2x0 C. tensile strength larger than 140 kg/mm2, preferably larger than 150 kg/mm2, further preferably larger than 152 kg/mm2. For the latter tensile strengths, 20xc2x0 C. V-notch impact values are preferably larger than 5 kgxc2x7m/cm2 and larger than 6 kgxc2x7m/cm2, respectively.
The present invention is a steam turbine blade made of a martensite steel having a 20xc2x0 C. V-notch impact value, wherein said 20xc2x0 C. V-notch impact value is larger than a value (y) (kgxc2x7m/cm2) calculated by an equation y=xe2x88x920.44x+68, preferably y=xe2x88x920.44x+71, further preferably y=xe2x88x920.44x+72, where (x) is a 20xc2x0 C. tensile strength (kg/mm2).
It is preferable that the steam turbine blade described above is made of a martensite steel containing C of 0.13-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; Mo of 1.5-4%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35; and N of 0.04-0.15%, on the basis of weight.
The present invention is characterized by a steam turbine blade, which is made of a martensite steel containing C of 0.19-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; Mo of 1.5-4%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35; and N of 0.04-0.15%, on the basis of weight.
The steam turbine blade described above is characterized by that the matensite steel contains C of 0.25-0.40% and Mo of 1.5-2.0%; or C of 0.19-0.40% and Mo of 3-4%, on the basis of weight.
The present invention is characterized by a steam turbine blade having a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, which is made of a martensite steel containing C of 0.16-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35%; and N of 0.04-0.15%, on the basis of weight.
The present invention is characterized by a steam turbine blade having a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, which is made of a martensite steel containing C of 0.13-0.40%; Si less than 0.5%; Mn less than 1.5%; Ni of 2-3.5%; Cr of 8-13%; at least one kind of Nb and Ta of 0.02-0.3% in total; V of 0.05-0.35%; and N of 0.04-0.15%, on the basis of weight, wherein a combination of the amount of C and the amount of Mo falls within a range formed by connecting to points A (0.21%, 1.5%), B (0.15%, 2.5%), C (0.15%, 3.2%) and D (0.25%, 4.0%). Further, it is preferable that the combination of the amount of C and the amount of Mo falls within a range formed by connecting to points E (0.39%, 1.9%), F (0.21%, 2.4%) and G (0.25%, 3.90%).
The present invention is characterized by a steam turbine power generating plant comprising a high pressure turbine, an intermediate pressure turbine and one or two low pressure turbines connected in tandem or cross, wherein blades in a final stage of the low pressure turbine are the steam turbine blades described in any one of the above items.
The present invention is characterized by a steam turbine power generating plant comprising a set of a high pressure turbine and a low pressure turbine and a generator; and a set of an intermediate pressure turbine and a low pressure turbine and a generator, the sets being connected in tandem or cross, wherein blades in a final stage of the low pressure turbines are the steam turbine blades described in any one of the above items.
The present invention is characterized by a low pressure steam turbine comprising a rotor shaft; rotor blades mounted on the rotor shaft; fixed blades for guiding flow of steam to the rotor blades; and a casing holding the fixed blades, wherein the rotor blades in a final stage are the steam turbine blades described in any one of the above items.
The present invention is characterized by a low pressure steam turbine having a rotating speed of 3000 rpm or 3600 rpm, which comprises five stages of the rotor blades symmetrically arranged in both sides, and is of a double flow construction having the rotor blades in the first stages being mounted in a middle portions of the rotor shaft, and the rotor blades in the final stages are the steam turbine blades described in any one of the above items.
It is preferable that the rotor shaft is made of a bainite steel having a 0.02% yield strength at room temperature above 80 kg/mm2 in the central portion of the rotor shaft; 0.2% yield strength above 87.5 kg/mm2 or a tensile strength above 92 kg/mm2; and a FATT below xe2x88x925xc2x0 C. or a 20xc2x0 C. V-notch impact value above 10 kgxc2x7m.
It is preferable that the bainite steel is a forged steel containing C of 0.20-0.28%; Si less than 0.15%; Mn less than 0.25%; Ni of 3.25-4.25%; Cr of 1.6-2.5%; Mo of 0.25-0.6%; and V of 0.05-0.20%, on the basis of weight.
In regard to the steam turbine blade in accordance with the present invention, it is preferable that the material required for the steam turbine blade having a blade length above 46 inches for a 3000 rpm turbine or a blade length above 38.5 inches for a 3600 rpm turbine has a 20xc2x0 C. tensile strength above 147 kg/mm2 and a 0.02% yield strength above 101 kg/mm2.
In regard to the steam turbine blade in accordance with the present invention, an inclination of the blade portion in the width direction is nearly parallel to an axial direction of the rotor shaft at a position of the implanting portion, the top end portion of the blade is inclined to the axial direction preferably from 65 to 85 degrees, further preferably from 70 to 80 degrees.
The steam turbine blade in accordance with the present invention has a blade length above 45 inches for a 3000 rpm turbine or a blade length above 37.5 inches for a 3600 rpm turbine, and it is preferable that the implanting portion is of a fork shape having nine or more prongs for the blade above 45 inch length and seven or more prongs for the blade above 37.5 inch length, or of an inverse Christmas tree shape having four or more projections.
In the steam turbine blade in accordance with the present invention, it is preferable that the width of the implanting portion is 2.1 to 2.5 times as large as the width of the top end of the blade portion.
In the present invention, it is preferable that the steam turbine blade has an erosion preventive shield arranged in the leading side of the top end portion of the blade portion; the implanting portion of a fork type; and holes to insert a pin therein for fixing the blade to the rotor shaft in plural stages, the diameter of the hole being larger in the blade side than the opposite side.
The low pressure turbine has the final stage rotor blade of which the average diameter is above 3520 mm, preferably 3600-3750 mm for the 3000 rpm turbine, and above 2930 mm, preferably 3000-3130 mm for the 3600 rpm turbine.
The low pressure turbine has the final stage rotor blade of which the average diameter is above 2800 mm, preferably 3000-3040 mm for the 3000 rpm turbine, and above 2330 mm, preferably 2400-2530 mm for the 3600 rpm turbine.
The above requirements can be applied to the following invention.
In the present invention, it is preferable that in the steam turbine power generating plant described above, when the steam inlet temperature to the first stage rotor blades of the high pressure turbine and the intermediate pressure turbine or the high and intermediate pressure turbine is within a rage of 538 to 660xc2x0 C. (538xc2x0 C., 566xc2x0 C., 593-605xc2x0 C., 610-620xc2x0 C., 620-630xc2x0 C., 630-640xc2x0 C.) and the steam inlet temperature to the first stage rotor blades of the low pressure steam turbine is within a rage of 350 to 400xc2x0 C., the rotor shaft or all of the rotor shaft, the rotor blades, the fixed blades and the inner casing exposed to the above-mentioned steam inlet temperature of the high pressure turbine and the intermediate pressure turbine or the high and intermediate pressure turbine are made of a high strength martensite steel containing Cr of 8 to 13 weight %, and the rotor blades in the first stage or up to the second stage or the third stage among the above components are made of a nickel base alloy.
In the present invention, it is preferable that in a high pressure steam turbine, an intermediate pressure turbine or a high and intermediate pressure integrated steam turbine in which outlet steam from a high pressure side turbine is heated up to a temperature equal to or above an inlet temperature of the high pressure side turbine to be conducted to an intermediate pressure side turbine, the steam turbine comprises a rotor shaft; rotor blades mounted onto the rotor shaft; fixed blades for guiding steam to flow into the rotor blades; and an inner casing for holding the fixed blades, wherein the steam flowing into the first stage of the rotor blades has a temperature of 538 to 660xc2x0 C. and a pressure above 250 kgf/cm2 (preferably 246 to 316 kgf/cm2) or 170 to 200 kgf/cm2, and the rotor shaft or the rotor shaft and the rotor blades and the fixed blades at least in the first stage are made of a high strength martensite steel having fully annealed martensite structure containing Cr of 8.5 to 13 weight % (preferably 10.5 to 11.5 weight %) of which the 105 hour creep rupture strength at a temperature corresponding to each of the steam temperatures (538xc2x0 C., 566xc2x0 C., 610xc2x0 C., 625xc2x0 C., 640xc2x0 C., 650xc2x0 C., 660xc2x0 C.) is above 10 kgf/mm2 (preferably, above 17 kgf/mm2), and the rotor blades in the first stage or up to the second stage or the third stage among the above components are made of a nickel base alloy, and the inner casing is made of a martensite cast steel containing Cr of 8 to 9.5 weight % of which the 105 hour creep rupture strength at a temperature corresponding to each of the steam temperatures is above 10 kgf/mm2 (preferably, above 17 kgf/mm2).
In the high pressure steam turbine, the intermediate pressure turbine or the high and intermediate pressure integrated steam turbine, in order to cope with the steam temperature of 593-660xc2x0 C., it is preferable that at least one of the rotor shaft or the rotor blades and the fixed blades in the first stage are made of a high strength martensite steel containing c of 0.05-0.20%; Si less than 0.6%, preferably less than 0.15%; Mn less than 1.5%, preferably 0.05-1.5%; Cr of 8.5-13%, preferably 9.5-13%; Ni of 0.05-1.0%; V of 0.05-0.5%, preferably 0.05-0.35%; at least one kind of Nb and Ta of 0.01-0.20%; N of 0.01-0.1%, preferably 0.01-0.06%; Mo less than 1.5%, preferably 0.05-1.5%; W of 0.1-4.0%, preferably 1.0-4.0%; Co less than 10%, preferably 0.5-10%, B less than 0.03%, preferably 0.0005-0.03%; and Fe above 78%, on the basis of weight. In order to cope with the steam temperature lower than 600-620xc2x0 C., it is preferable that at least one of the rotor shaft or the rotor blades and the fixed blades in the first stage are made of a high strength martensite steel containing c of 0.1-0.25%; Si less than 0.6%; Mn less than 1.5%; Cr of 8.5-13%; Ni of 0.05-1.0%; V of 0.05-0.5%; W of 0.10-0.65%; at least one kind of Nb and Ta of 0.01-0.20%; Al less than 0.1%; Mo less than 1.5%; N of 0.025-0.1%; and Fe above 80% on the basis of weight. It is preferable that the inner casing is made of a high strength martensite steel containing c of 0.06-0.16%; Si less than 0.5%; Mn less than 1%; Ni of 0.2-1.0%; Cr of 8-12%; V of 0.05-0.35%; at least one kind of Nb and Ta of 0.01-0.15%; N of 0.01-0.8%; Mo less than 1%; W of 1-4%; B of 0.0005-0.003%; and Fe above 85%, on the basis of weight.
It is preferable that the high pressure steam turbine in accordance with the present invention has seven or more stages of the rotor blades, preferably nine or more stages, further preferably nine to twelve stages; a double flow structure in the first stage; and a distance (L) between the centers of bearing of the rotor shaft longer than 5000 mm (preferably, 5100 to 6500 mm). It is preferable that the lengths of the blades from the first stage to the final stage are 25 to 180 mm.
It is preferable that the intermediate pressure steam turbine in accordance with the present invention symmetrically has six or more stages of the rotor blades, preferably six to nine stages; a double flow structure in the first stage disposed in the middle portion of the rotor shaft; and a distance (L) between the centers of bearing of the rotor shaft is longer than 5000 mm (preferably, 5100 to 6500 mm). It is preferable that the lengths of the blades are 60 to 300 mm.
It is preferable that the low pressure steam turbine in accordance with the present invention symmetrically has five or more stages of the rotor blades, preferably more than six stages, further preferably eight to ten stages; a double flow structure in the first stage disposed in the middle portion of the rotor shaft; and a distance (L) between the centers of bearing of the rotor shaft is longer than 6500 mm (preferably, 6600 to 7500 mm). It is preferable that the lengths of the blades are 90 mm in the first stage and the aforementioned length in the final stage.
In the rotor material for the high pressure, the intermediate pressure and the high and intermediate pressure turbines in accordance with the present invention, in order to attain a high high-temperature strength and a high low-temperature toughness and a high fatigue strength as the fully annealed martensite steel, the composition is preferably adjusted so that a Cr equivalent becomes 4 to 8.
Cr equivalent=Cr+6Si+4Mo+1.5W+11V+5Nbxe2x88x9240Cxe2x88x9230Bxe2x88x922Mnxe2x88x924Nixe2x88x922Co+2.5Ta
It is preferable that the high and intermediate pressure integrated steam turbine in accordance with the present invention has seven or more stages of the high pressure side rotor blades, preferably eight or more stages; five or more stages of the intermediate pressure side rotor blades, preferably six or more stages; and a distance (L) between the centers of bearing of the rotor shaft longer than 6000 mm (preferably, 6100 to 7000 mm). It is preferable that the lengths of the blades are 25 to 200 mm in the high pressure side and 100 to 350 mm in the intermediate pressure side.
The steam turbine blade in accordance with the present invention must be high in tensile strength and at the same time high in high cycle fatigue strength in order to withstand a high centrifugal force and a vibration stress caused by high speed rotation. Therefore, it is preferable that the metallic structure of the blade material is a fully annealed martensite structure because the fatigue strength is largely deteriorated when there exists a harmful xcex4-ferrite phase.
The component of the steel in accordance with the present invention is necessary to be adjusted so that the xcex4-ferrite phase is practically not contained by setting the Cr equivalent calculated by the aforementioned equation to a value smaller than 10, preferably 4 to 10.
As the heat treatment of controlling homogeneity in order to obtain the steam turbine long blade having homogeneity and high strength, it is preferable that the material is quenched by heating and holding it at 1000xc2x0 C. to 1100xc2x0 C. (preferably, 1000xc2x0 C. to 1055xc2x0 C.) for 0.5 to 3 hours after melting and forging and after that rapidly cooling it down to room temperature (particularly, oil quenching is preferable), and then annealed at 540xc2x0 C. to 620xc2x0 C., particularly it is preferable to perform twice or more annealing heat treatments of the first annealing of heating and holding the material 540xc2x0 C. to 570xc2x0 C., preferably for 1 to 6 hours and after that cooling it down to room temperature and the second annealing of heating and holding the material at 560xc2x0 C. to 590xc2x0 C. preferably for 1 to 6 hours and after that cooling it down to room temperature. It is preferable that the temperature of the second annealing is higher than the temperature of the first annealing, particularly by 10 to 30xc2x0 C., further preferable by 15 to 20xc2x0 C. It is further preferable to perform cryogenic treatment to cool the material down to the dry-ice temperature or the liquid nitrogen temperature in order to fully decompose the residual austenite phase.
As described above, the low pressure steam turbine blade in the final stage in accordance with the present invention has the blade length above 952.5 mm (37.5 inches), preferably 1016 mm (40 inches) to 1067 mm (42 inches) for the 3600 rpm turbine and the blade length above 1168.4 mm (46 inches), preferably 1219.2 mm (48 inches) to 1270 mm (50 inches) for the 3000 rpm turbine.
The martensite steel contains C above 0.13% in order to obtain high tensile strength and high toughness, but the toughness is decreased when the content of C exceeds 0.4%. Particularly, it is preferable that the content of C is set to a value within the range of 0.13 to 0.40%, 0.19 to 0.40% or 0.25 to 0.40% depending on the relationship with the content of Mo.
Si is a deoxidizing agent and Mn is a desulfurizing and deoxidizing agent, and the both are added to steel when the steel is melted, and a small amount of Si and Mn addition is effective. Si is a xcex4-ferrite forming element, and a large amount of the Si addition produces xcex4-ferrite to decrease the fatigue strength and the toughness. Therefore, it is preferable that an amount of Si addition is less than 0.5%, preferably less than 0.25%. In a case of using the carbon vacuum deoxidizing method or the electro-slug melting method, no addition of Si is preferable because there is no need to add Si. Particularly, the content of Si is preferably less than 0.10, further preferable less than 0.05%.
A small amount of Mn addition increases the toughness though a large amount of Mn addition decreases the toughness, and accordingly the content of Mn is preferably less than 1.5%. Particularly, although Mn is effective as a deoxidizing agent, the content of Mn is less than 0.4% from the view point of improving the toughness, preferably 0.05 to 0.2%.
Cr increases corrosion resistance and tensile strength, but forms xcex4-ferrite structure when it is added above 13%. Since the corrosion resistance and the tensile strength are insufficient when the content of Cr is less than 8%, it is preferable that the content of Cr is 10.5 to 12.5% particularly from the view point of the strength, further preferable 11 to 12%.
Mo is effective in increasing the tensile strength by a solution treated reinforce and a precipitating reinforce effects. Since the effect of improving the tensile strength is insufficient when the content of Mo is below 1.5% and the xcex4-ferrite structure is formed when the content of Mo exceeds 4%, it is preferable that the content of Mo is 1.5 to 2.0%, 2.0 to 3.5%, 3 to 4% depending on the content of C. In addition, since W also has the same effect as that of Mo, the content of Mo may be less than 2% by replacing part of Mo by W in order to improve the tensile strength.
V and Nb have an effect to increase the tensile strength and to improve the toughness by precipitating carbide. Since the effect is insufficient when V is less than 0.05% and Nb is less than 0.02%, it is preferable that V is less than 0.35% and Nb is less than 0.3% from the view point of avoiding the xcex4-ferrite formation. Particularly, it is preferable that the content of V is 0.15 to 0.30%, further preferable 0.25 to 0.30%, and the content of Nb is 0.10 to 0.20%, further preferable 0.12 to 0.18%. Ta may be similarly added instead of Nb, and the amount in the complex addition may be equal to the above content in total.
Ni has increases the low-temperature toughness and also has an effect of preventing the xcex4-ferrite formation. This effect is insufficient when the content of Ni is less than 2%, and is saturated when the addition exceeds 3.5%. Particularly, it is preferable that the content of Ni is 2.6 to 3.2%.
N improves the tensile strength and has an effect of preventing xcex4-ferrite formation, but the effect is insufficient when the content of N is less than 0.04% and the toughness is decreased when the content exceeds 0.15%. Particularly, an excellent property can be attained when the content of N is within the range of 0.06 to 0.10%.
Since reducing contents of P and S has an effect to increase the low-temperature toughness without deteriorating the tensile strength, it is preferable that the contents are reduced as low as possible. It is preferable from the viewpoint of improving the low-temperature toughness that the content of P is less than 0.015% and the content of S is less than 0.015%. Particularly, it is preferable that the content of P is less than 0.010% and the content of S is less than 0.010%.
Since reducing contents of Sb, Sn and As also has an effect to increase the low-temperature toughness, it is preferable that the contents are reduced as low as possible. However, from the viewpoint of the level of the steel manufacturing technology at present, the content of Sb is limited less than 0.0015%, the content of Sn is limited less than 0.01% and the content of As is limited less than 0.02%. Particularly, it is preferable that the content of Sb is less than 0.001%, the content of Sn is less than 0.005% and the content of As is less than 0.01%.
Further, in the present invention, it is preferable that the martensite steel contains one kind or each of combinations of two kinds, three kinds or four kinds of MC metal carbide forming elements such as Ti, Zr, Hf, Ta and so on less than 0.5% in total. In addition, in order to improve the plasticity workability and the toughness, the martensite steel contains at least one kind of Al, Ca, Mg, Y, and rear earth elements less than 0.2% in total.
As the heat treatment of the material in accordance with the present invention, it is preferable that the fully annealed martensite structure is obtained by uniformly heating it at a temperature high enough to change it to fully austenite phase from 1000xc2x0 C. at the minimum to 1100xc2x0 C. at the maximum and after that rapidly cooling it down to room temperature (preferably, oil quenching), and then annealed the material by heating and holding the material 550xc2x0 C. to 570xc2x0 C. and after that cooling it down (the first annealing) and heating and holding the material 560xc2x0 C. to 680xc2x0 C. and after that cooling it down (the second annealing). It is preferable that the temperature of the second annealing is higher than the temperature of the first annealing.
It is preferable that an erosion preventive layer made of a Co base alloy is attached to a top end leading edge portion of the rotor blade in the final stage. It is preferable that a plate made of the Co base alloy containing Cr of 25 to 30%, W of 1.5 to 7.0% and C of 0.5 to 1.5% on the weight basis is welded to the top end leading edge portion of the rotor blade through electron beam welding or TIG welding.
(2) It is preferable that the rotor shaft of the high pressure, the intermediate pressure or the high and intermediate pressure integrated type steam turbine in accordance with the present invention has an overlay weld layer made of a Crxe2x80x94Mo low-alloy steel having high bearing property formed on the journal portion. The overlay weld layer is composed of plural layers from 3 layers to 10 layers formed by welding materials, and contents of Cr in the welding materials are successively reduced from the first layer to a layer between the second layer to the fourth layer, and the layers from the fourth layer on are welded using welding materials made of steels having the same Cr content, and the Cr content in the welding material used for welding the first layer is less than the Cr content in the base material by 2 to 6 weight %, and the Cr contents in the welded layers from the fourth layer on are set to 0.5 to 3 weight % (preferably, 1 to 2.5 weight %).
In the present invention, in order to improve the bearing property of the journal portion, the overlay weld layer is preferable from the viewpoint of the highest safety. It is also possible to employ a shrink-in structure of a sleeve made of a low-alloy steel containing Cr of 1 to 3 weight %.
Number of the welding layers for gradually decreasing the Cr content is preferably 3 or more, but the additional effect can not be obtained if number of the layers is increased above 10 or more. For example, the thickness of the overlay weld layer is required to be approximately 18 mm in the final finishing. In order to forming the overlay weld layer having such a thickness, it is preferable that the overlay weld layer is composed of at least five layers excluding a margin for the final finishing by cutting. It is preferable that the layers from the third layer on have mainly have an annealed martensite structure and precipitation of carbide. Particularly, it is preferable that the material of the welded layers from the fourth layer on contains C of 0.01 to 0.1%, Si of 0.3 to 1%, Mn of 0.3 to 1.5%. Cr of 0.5 to 3%, Mo of 0.1 to 1.5% on the weight basis, and the remainder of Fe.
(3) It is preferable to use a martensite group heat resistant steel for constructing the components of the high pressure steam turbine, the intermediate pressure steam turbine and the high and intermediate pressure steam turbine in accordance with the present invention such as a valve box of an inner casing control valve, a valve box of a combined reheater valve, a main steam lead pipe, a main steam inlet pipe, a reheater inlet pipe, a nozzle box of the high pressure turbine, a first stage diaphragm of the intermediate turbine, a main steam inlet flange and an elbow of the high pressure turbine, and a main steam stop valve.
The material used for constructing components of an ultra-super critical pressure turbine for an operating pressure above 250 kgf/cm2 such as a high pressure, an intermediate pressure or a high and intermediate pressure inner casing, and casings of a main steam stop valve and a control valve is required to have a 105 hour creep rupture strength at the operating temperature above 9 kgf/mm2 and a room temperature impact absorption energy above 1 kgf-m.
It is preferable that the inner casing material is a martensite cast steel containing C of 0.06 to 0.16% (preferably 0.09 to 0.14%), N of 0.01 to 0.1% (preferably 0.02 to 0.06%), Mn less than 1% (preferably 0.4 to 0.7%), Si-free or Si less than 0.5% (preferably 0.1 to 0.4%), V of 0.05 to 0.35% (preferably 0.15 to 0.25%), Nb less than 0.15% (preferably 0.02 to 0.1%), Ni of 0.2 to 1% (preferably 0.4 to 0.8%), Cr of 8 to 12% (preferably 8 to 10%, further preferably 8.5 to 9.5%), W of 1 to 3.5%, Mo less than 1.5% (preferably 0.4 to 0.8%) on the weight basis and the remainder of Fe.
It is preferable that the content of W is 1.0 to 1.5% for 620xc2x0 C., 1.6 to 2.0% for 630xc2x0 C., 2.1 to 2.5% for 640xc2x0 C., 2.6 to 3.0% for 650xc2x0 C., and 3.1 to 3.5% for 660xc2x0 C.
Addition of Ta, Ti and Zr has an effect to increase the toughness, and the effect can be sufficiently attained by adding Ta less than 0.15%, Ti less than 0.1% and Zr less than 0.1% solely or in complex. When Ta is added above 0.1%, the addition of Nb can be omitted.
(4) It is preferable that the rotor shaft of the low pressure steam turbine is made of a low-alloy steel having fully annealed bainite structure containing C of 0.2 to 0.3%, Si less than 0.15%, Mn less than 0.25%, Ni of 3.25 to 4.25%, Cr of 1.6 to 2.5%, Mo of 0.25 to 0.6%, V of 0.05 to 0.25% and Fe more than 92.5% on the basis of weight, and is manufactured through the method similar to that of the rotor shaft of the high pressure and the intermediate pressure turbines. Particularly, it is preferable that the low-alloy steel contains Si less than 0.05%, Mn less than 0.1% and the other impurities such as P, S, As, Sb, Sn and so on less than 0.025% in total, preferably less than 0.015%, so as to suppress the impurities as low as possible by using a material produced though a super-cleaned process using a raw material containing less impurities. It is preferable that the low-alloy steel contains P and S each less than 0.010%, Sn and As each less than 0.005% and Sb less than 0.001%. The rotor shaft has a close relationship with the rotor blade in the final stage made of the martensite steel having the above mentioned specified length corresponding to the rotation speed. The rotor shaft in accordance with the present invention is as to be described later in the embodiment. It is preferable that the rotor shaft in accordance with the present invention with a center hole has a fork shape implanting portion, and the rotor shaft without the center hole has an inverse Christmas tree shape implanting portion.
(5) It is preferable that the turbine blades other than in the final stage and the nozzles of the low pressure turbine are made of a fully annealed martensite steel containing C of 0.05 to 0.2%, Si of 0.1 to 0.5%, Mn of 0.2 to 1.0%, Cr of 10 to 13%, and Mo of 0.04 to 0.2%.
(6) It is preferable that the inner and the outer casings of the low pressure turbine are made of a carbon cast steel containing C of 0.2 to 0.3%, Si of 0.3 to 0.7%, and Mn less than 1%.
(7) It is preferable that the casing of the main steam stop valve and the casing of the steam control valve are made of a fully annealed martenasire steel containing C of 0.1 to 0.2%, Si of 0.1 to 0.4%, Mn of 0.2 to 1.0%, Cr of 8.5 to 10.5%, Mo of 0.3 to 1.0%, W of 1.0 to 3.0%, V of 0.1 to 0.3%, Nb of 0.03 to 0.1%, N of 0.03 to 0.08%, and B of 0.0005 to 0.003%.
(8) It is preferable that the outer casings of the high pressure turbine, the intermediate turbine and the high and intermediate turbine are made of a cast steel having bainite structure and containing C of 0.10 to 0.20%, Si of 0.05 to 0.6%, Mn of 0.1 to 1.0%, Ni of 0.1 to 0.5%, Cr 1 to 2.5%, Mo 0.5 to 1.5%, V of 0.1 to 0.35%, and preferably Al less than 0.025%, at least one of B of 0.0005 to 0.004% and Ti of 0.05 to 0.2%. Particularly, is preferable that the outer casings the cast steel containing C of 0.10 to 0.18%, Si of 0.20 to 0.60%, Mn of 0.20 to 0.50%, Ni of 0.1 to 0.5%, Cr of 1.0 to 1.5%, Mo of 0.9 to 1.2%, V of 0.2 to 0.3%, Al of 0.001 to 0.005%, Ti of 0.045 to 0.10%, and B of 0.0005 to 0.0020%. It is further preferable that the ratio Ti/Al is 0.5 to 10.
(9) Instead of the martensite steel described above, the blades in the first stage of the high pressure turbine, the intermediate pressure turbine and the high and intermediate pressure turbine (the high pressure side and the intermediate pressure side) under a steam temperature of 625 to 650xc2x0 C., preferably the blades up to the second stage or the third stage of the high pressure turbine and the high pressure side of the high and intermediate pressure turbine and blades up to the second stage of the intermediate pressure turbine and the intermediate pressure side of the high and intermediate pressure turbine, may be made of a Ni base alloy containing C of 0.03 to 0.20% (preferably 0.03 to 0.15%), Cr of 12 to 20%, Mo of 9 to 20% (preferably 12 to 20%), Co less than 12% (preferably 5 to 12%), Al of 0.5 to 1.5%, Ti of 1 to 3%, Fe less than 5%, Si less than 0.3%, Mn less than 0.2%, B of 0.003 to 0.015%, in addition to the above compositions, at least one kind of Mg less than 0.1%, rare earth element less than 0.5% and Zr less than 0.5%, on the weight basis. The content of the above additional compositions include 0%. The blades are solution treated and aging treated after being forged.